The preferred embodiments are in the field of magnetic storage media drives and are more specifically directed to a disk drive with multiple level power reduction during write operations.
Magnetic disk drives are used over a wide range of electronic systems, including large-scale network servers, desktop computers and workstations, portable computers (e.g., laptops), and now even in modern handheld devices such as portable digital audio players. As is well known in the art, the capacity of disk drives has greatly increased over recent years, at ever decreasing cost per megabit, while at the same time the size of the drive continues to decrease. Indeed, the decrease in size permits the use of drives in smaller equipment, including the above-mentioned audio players and with likely additional applications in the future.
The decrease in disk drive size has been achieved in many ways, including the use of smaller parts and the dimensions between those parts. A relatively smaller drive includes a smaller disk or a stack of smaller disks arranged in a so-called head stack, where the axis of each disk is co-aligned and an arm is typically located between each disk as well as on top of the uppermost disk and below the lowermost disk. The arms support one or more read/write sensor assemblies (or “heads”) for read/write operations with respect to the disk adjacent a respective sensor assembly. In addition, often integrated circuits are included within the drive, where one common integrated circuit is the drive preamplifier, which communicates electrical signals to each sensor assembly so as to accomplish data read and write operations. The marketplace has dictated the reduction in size of this and sometimes other circuits to reduce the drive size, and also to reduce overall cost. One skilled in the art will appreciate other manners in which drive sizes have been reduced.
Various factors such as the materials, dimensions, proximity, and component interfaces of the above and related components provide increasing heat in device drives. For example, the movable arms that support the sensor assemblies as well as the arm-supporting movable member (sometimes referred to as an E-block) are typically metal of varying sizes and those sizes as well as spacing between them may be small if not microscopic in dimensions. As another example, the entire E-block, and correspondingly the arms it supports, is rotated within an arc by a mechanism that typically includes a coil with magnets above and below the coil so that a reversible current through the coil can cause a partial rotation of the mechanism in either direction across the arc. The current to operate the coil, and the current provided by the preamplifier to write data to the disk, and to a lesser extent to read from a disk, also generates heat. As still another example, with physical contact between certain components there is little, if any, air gap and, thus air is trapped and therefore is unable to efficiently release heat in such an area. In other words, there is simply little or no room for convection cooling and there is heat transfer between components. Various other factors also contribute to the accumulation of heat in and near the head stack assembly. With larger media, the movable arms must be longer and therefore require a greater amount of current to drive the inductance of the above-mentioned coils, thereby creating more heat. Further, the dimensions of the arms may reduce the ability to dissipate heat. As another example, the generation of heat increases with power demands required to support increasing revolutions per minute of the media as well as increasing data rates, such as 800 to 900 mbps in contemporary laptops. Still further, high power is required to support the transition between write and read operations, with a greater power demand in the transition from write to read. Still other examples may be appreciated by one skilled in the art.
Heat build-up in and near the head stack assembly is undesirable for many reasons. For example, long term heat exposure affects the lifespan of the unit, such as in connection with the deleterious effect that heat has on the silicon used to form the integrated circuit preamplifier. As known in the integrated circuit art, the reliability and lifespan of an integrated circuit are reduced at higher temperatures, and the reductions will be exponential as temperatures reach a certain level or range. Indeed, as the preamplifier integrated circuit is reduced in size, the electrical current is forced to occupy a smaller area and, as a result, higher temperatures, including higher junction temperatures, are incurred on the preamplifier and exacerbate the above considerations. As another example, the accumulation of heat necessarily limits the speed at which the drive may be operated, since exceeding a determined limit will cause still more heat and affect lifespan and data integrity. In some applications, these factors may be less critical, whereas in others the demands of the marketplace are extremely high, so such factors are paramount and therefore so are the above-noted considerations. Additionally, certain applications may be more write intensive (e.g., personal video recorders), and since the write operation uses more power consumption than the read operation, these write-intensive applications expose the drive to longer periods of heat in use versus a less write-intensive application.
With all of the attributes described, the present inventors seek to improve upon aspects related to the above and more specifically endeavor to reduce power consumption, and the corresponding heat generated by such consumption, in a disk drive. With such reduction, various benefits may be achieved. For example, for a given speed of operation and with a relative reduction in power consumption and heat, then the lifespan and reliability of the integrated circuit is improved. As another example, with a technique that reduces power consumption from an acceptable level to a lower level, then there is margin between the lower level and the acceptable level, and that margin may be re-used by increasing the read/write speed so that even though power consumption is increased from the lower level, it is workable as it still remains at or below the acceptable level. These and other benefits will be appreciated by one skilled in the art in connection with the preferred embodiments detailed below.